Reaction of CO with a Methylpalladium Heterocyclic Carbene Complex: Product Decomposition RoutesImplications for Catalytic Carbonylation Processes

The methylpalladium−heterocyclic carbene dimer [PdMe(tmiy)(μ-Cl] 2 ( 1) (tmiy = 1,3,4,5-tetramethylimidazolin-2-ylidene) reacts with CO to yield [PdMeCl(tmiy)CO] ( 2 ) through cleavage of the Cl bridge. Complex 2 decomposes in solution to yield the 1,2,3,4,5-pentamethylimidazolium ion ( I ) along with a small amount of 2-acyl-1,3,4,5-tetramethylimidazolium ( II) . In the presence of AgBF 4 the dimer reacts with CO to give II as the major product. The reaction sequence is interpreted as evidence for CO insertion into the Pd−Me bond of 2 and also represents a possible mode of deactivation for potential CO/ethylene copolymerization catalysts based on heterocylic carbene complexes.